An ink jet head of the called on-demand type which spouts forth ink droplets in accordance with a print signal is categorized into two types according to the type of the ink discharging force generating means. The first type of the ink jet head is a called bubble jet type of the ink jet head in which a heater for instantaneously vaporizing ink is located at the nozzle tip, and ink droplets are generated and spouted forth by an expanding pressure when ink is vaporized. The second type of the ink jet head is constructed such that a part of an ink chamber forming an ink reservoir is constructed with a piezoelectric transducer which is deformed according to a print signal, and ink droplets are impelled to emit forward by a pressure generated in the ink chamber by the deformation of the piezoelectric transducer.
The on-demand type of the ink jet head as the second type of the ink jet head, as disclosed in Published Unexamined Japanese Patent Application Nos. Sho. 58-119870 and 58-119872, is constructed such that a vibrating film (called a diaphragm in both the publications) forming an ink chamber is coupled with a second end of a piezoelectric transducer fastened at a first end to a base, with an island-like protrusion (called a leg in both the publications) inserted therebetween. The expanding and contracting actions of the piezoelectric transducer cause the piezoelectric transducer to push the leg and to deform the vibrating film. The deformed film causes ink of the ink chamber to forcibly emit forward in the form of ink droplets through a nozzle opening.
Neither of the above-mentioned publications discloses any specific method of forming the vibrating film and the leg. The leg takes a complicated construction where it is fitted into a bearing. Therefore, it is very difficult to accurately manufacture and assemble the leg member and the bearing member for the purposes of size reduction and high density of packaging. To solve those problems, a first measure taken that is disclosed in Published Unexamined Japanese Patent Application No. Hei. 3-15555 is such that, as shown in FIG. 10, a vibrating film 61a (called a vibrating plate in the publication) made of silicon, 1.8 .mu.m thick, and an island-like protrusion 61b (called a protrusion in the same publication) made of silicon oxide, 100 .mu.m thick, are coupled together into a vibrating film 61 with a protrusion by the manufacturing technique of semiconductor elements, and the island-like protrusion 61b is brought into contact with a piezoelectric transducer 60.
In another measure taken by the publication, as a second measure, the island-like protrusion 61b is formed on the vibrating film 61a, 1 to 10 .mu.m thick, made of metal, such as nickel, stainless steel, iron, copper, silver, gold, tantalum, or titanium, by an electroforming method, and the island-like protrusion 61b is brought into contact with the piezoelectric transducer 60.
In yet another measure taken by the publication, as a third measure, the island-like protrusion 61b of which the material and the method are not disclosed is fastened to the vibrating film 61a as an organic material film of 50 .mu.m thick, and the island-like protrusion 61b is brought into contact with the piezoelectric transducer 60.
In a fourth measure taken by Published Unexamined Japanese Patent Application No. Hei. 3-190744, as shown in FIG. 11, a dummy layer, 100 .mu.m thick, is formed on an electrode 71c of a piezoelectric transducer 70, and the resultant structure is cut by dicing process. The piezoelectric transducer 70 is separated, by the dicing, to form a dummy layer on a island-like protrusion 73b. A vibrating film 73a (called a cover member in the publication) of approximately 50 .mu.m thick is bonded to the dummy layer island-like protrusion 73b by epoxy adhesive.
To realize a practical ink jet head by any of those conventional techniques, the following problems are created in addition to the difficulty of accurate manufacturing and assembly.
Firstly, the vibrating film 73, when formed of a high polymer resin of approximately 50 .mu.m thick, cannot transfer pushing pressure and displacement that are high enough to discharge ink, to an ink chamber 75. Even if Pb-zirconatetitante that is considered, at present, to have the highest transducing efficiency is used for the piezoelectric material of the piezoelectric transducer 70, the displacement achieved is several .mu.m or less. When a high polymeric resin film ten times or more as thick as the above displacement is used and it is pushed with the piezoelectric transducer 70, the displacement and pressure by pushing are absorbed by elastic deformation. Accordingly, it is not suitable for a recording head of a small size and high density of packaging. Secondly, vibrating film 61a formed of a silicon film or a metal foil is not resistive to the bending deformation. It will be fatigued and broken down. Therefore, it is not suitable for the displacement transfer member for the ink jet head which will repeat the deformation totally several hundred million times at high speed. Further, those materials are extremely high in rigidity. Because of this, they are not suitable as materials for the vibrating film which must be as flexible as possible.
With the view of solving the above problems, the present invention has an object to realize an ink jet head which is highly efficiently operable and to manufacture, at low cost, an ink jet head using a vibrating film with a protrusion, which enables the structure to be easily manufactured in a mass production manner.